Catalytic reduction of carbon-chromite composite pellets by lime

The catalytic effect of lime on the reduction of carbon-chromite composite pellets was investigated at 1270-1433 degrees C under CO-argon atmospheres. It was found that the data for the early stage of reduction, up to a reduction level of 30-60%, fit both an exponential law for nucleation control and an equation for chemical control with an apparent activation energy ranging from 139 to 161 kJ/mol depending on the amount of lime addition. In the late stage (after about 65% reduction), solid diffusion of chromium in the oxide phase is the most likely rate-controlling step with an apparent activation energy of 410 kJ/mol. Besides the possibility of it being able to go into the spinel lattice and release the FeO, lime is also suggested to catalyse the chromite reduction through enhancing the nucleation and/or interfacial reaction in the early stage, and facilitating the solid-diffusion process in the late stage. The results of this study also indicate that heat treatment of chromite has a significant effect on the reduction kinetics. (C) 1997 Elsevier Science B.V.